This patent application claims priority to provisional patent application 61/339,999 filed on Mar. 11, 2010 which is incorporated by reference herein.
There are many different engine cycles based on a piston/cylinder configuration. Each such engine is designed for a specific application. They differ widely in mode of operation, maximum size, engine speed, power output per unit mass, most suitable fuel and method of ignition. Engine fuel efficiency increases with: 1) compression ratio (CR) used; 2) ignition timing control; and 3) fuel combustion rate. A high rate of combustion maximizes combustion compression and minimizes piston ring and valve seat leakage. Many gasoline fueled piston engines are only able to ignite near stoichiometric mixtures and then at limited compression ratio. For decades automotive engineers have made improvements in Diesel fuel injected engines, Homogeneous Charge Spark Ignited Engines, and Homogeneous Charge Compression Ignition (HCCI) engines. HCCI technology eliminates the need for spark plugs and high pressure fuel injectors. However, ignition timing control has been successfully accomplished only over a narrow range in engine speed and load, and this only with the aid of complex computer control over the air/fuel mixture, exhaust gas recirculation (EGR), engine load, and engine speed. In 2009, Ford Motor Company and Mercedes Benz both incorporated a limited utilization of HCCI in their gasoline fueled automotive fleet which resulted in increased combustion rate and thus combustion compression, to improve fuel efficiency. Those computer controlled engines are able to take advantage of HCCI high combustion compression over a limited range of engine speed and power settings.
Recently, new accelerated compression cranking mechanisms have become available, which are capable of producing rapid piston movement near top dead center (TDC). This increases the rate of compression to auto-ignition, to reduce heat loss to the walls and the likelihood of engine knock. Stratifying the charge has been found to be effective but, unfortunately, has been difficult to accomplish at all loads. Accelerated compression ignition can be accomplished even without air inlet throttle valve, and ignite mixtures near TDC under various engine speeds and loads, as required for maximum combustion compression. High compression ratio enables rapid combustion of lean mixtures as needed to limit NOx formation, but this requires high work and torque input during compression to a high compression ratio. It is well known that reducing the combustion volume and flattening the geometry of the combustion chamber during compression ignition significantly reduces the number of independent ignition centers which lead to engine knock and also minimizes the combustion volume and likelihood of engine knock. This invention avoids a complex cranking mechanism. It requires only a conventional reciprocating engine, with near sinusoidal piston motion. In one embodiment, upper cylinder wall cavities are made by machining a shallow tapered groove, beyond the cylinder wall and connecting this groove by multiple ports to the cylinder inside. In one embodiment, those cavities are sized to equal about half the clearance volume above the piston, at the time the upper two piston rings seal off those wall cavities. The result is doubling the compression ratio from 10:1 to 20:1 when piston reached TDC. This results in timed compression ignition as needed for HCCI use. The air/fuel mixture sealed off inside those cavities is ignited when the piston enters its expansion stroke and exposes those cavities. The slope of the cavity groove facilitates cleaning when the head is removed.